1. Field of the Invention
This invention relates generally to radar exciter architectures and more particularly, to an exciter including a wide-band digital waveform generator which simplifies the circuitry employed in a multi-mode radar.
2. Description of Related Art
An exciter block diagram for a conventional multi-mode radar requiring a wide variety of waveforms is shown in FIG. 1. The exciter shown in FIG. 1 includes a master oscillator 10, a reference frequency generator 12 which generates a synchronizer clock signal and two of three receiver local oscillator signals LO2 and LO3, a narrowband waveform generator(s) 14, frequency upconversion circuitry 16 which generates the third local oscillator signal LO1 and a transmit timing (PRF) signal, a wideband waveform generator 18 and a frequency synthesizer 20.
Wideband waveforms required by the radar and generated by the wideband waveform generator 18 utilizes direct digital synthesis (DDS) techniques while the frequency synthesizer 20 provides frequency synthesis by direct analog synthesis (DAS). The DAS technique uses mixers, filters and switches, not shown, to select combinations of various CW frequencies to generate the required frequencies for radar frequency agility. It should be noted, however, that when desirable, other types of frequency synthesizers, such as indirect frequency synthesizers, can be used.
The benefits of direct analog synthesis DAS are low phase-noise and fast switching. However, this technique typically requires an expensive and complex complement of microwave hardware which adversely affects size, weight, power, and cost. New radar systems, on the other hand, now have an inherent requirement to reduce size, weight, power and cost.